41594B datasheet(178/372 Pages) MICROCHIP

178 / 372 page

PIC12LF1840T48A

DS41594B-page 178

Preliminary

 2011-2012 Microchip Technology Inc.

23.1

DSM Operation

The DSM module can be enabled by setting the MDEN

bit in the MDCON register. Clearing the MDEN bit in the

MDCON register, disables the DSM module by auto-

matically switching the carrier high and carrier low sig-

nals to the VSS signal source. The modulator signal

source is also switched to the MDBIT in the MDCON

inactive, but that it is also consuming the least amount

of current.

The values used to select the carrier high, carrier low,

and modulator sources held by the Modulation Source,

Modulation High Carrier, and Modulation Low Carrier

control registers are not affected when the MDEN bit is

cleared and the DSM module is disabled. The values

inside these registers remain unchanged while the

DSM is inactive. The sources for the carrier high, car-

rier low and modulator signals will once again be

selected when the MDEN bit is set and the DSM

module is again enabled and active.

The modulated output signal can be disabled without

shutting down the DSM module. The DSM module will

remain active and continue to mix signals, but the out-

put value will not be sent to the MDOUT pin. During the

time that the output is disabled, the MDOUT pin will

remain low. The modulated output can be disabled by

clearing the MDOE bit in the MDCON register.

23.2

Modulator Signal Sources

The modulator signal can be supplied from the

following sources:

• CCP1 Signal

• MSSP1 SDO1 Signal (SPI mode only)

• Comparator C1 Signal

• EUSART TX Signal

• External Signal on MDMIN pin

• MDBIT bit in the MDCON register

The modulator signal is selected by configuring the

MDMS <3:0> bits in the MDSRC register.

23.3

Carrier Signal Sources

The carrier high signal and carrier low signal can be

supplied from the following sources:

• CCP1 Signal

• Reference Clock Module Signal

• External Signal on MDCIN1 pin

• External Signal on MDCIN2 pin

•VSS

The carrier high signal is selected by configuring the

MDCH <3:0> bits in the MDCARH register. The carrier

low signal is selected by configuring the MDCL <3:0>

bits in the MDCARL register.

23.4

Carrier Synchronization

During the time when the DSM switches between car-

rier high and carrier low signal sources, the carrier data

in the modulated output signal can become truncated.

To prevent this, the carrier signal can be synchronized

to the modulator signal. When synchronization is

enabled, the carrier pulse that is being mixed at the

time of the transition is allowed to transition low before

the DSM switches over to the next carrier source.

Synchronization is enabled separately for the carrier

high and carrier low signal sources. Synchronization for

the carrier high signal can be enabled by setting the

MDCHSYNC bit in the MDCARH register. Synchroniza-

tion for the carrier low signal can be enabled by setting

the MDCLSYNC bit in the MDCARL register.

Figure 23-1 through Figure 23-5 show timing diagrams

of using various synchronization methods.

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